A horizontal $\mathrm{p}?\mathrm{i}?\mathrm{n}$ ridge waveguide emitter on a silicon (100) substrate with a ${\mathrm{Ge}}_{0.91}{\mathrm{Sn}}_{0.09}/\mathrm{Ge}$ multi-quantum-well (MQW) active layer was fabricated by molecular beam epitaxy. The device structure was designed to reduce light absorption of metal electrodes and improve injection efficiency. Electroluminescence (EL) at a wavelength of 2160 nm was observed at room temperature. Theoretical calculations indicate that the emission peak corresponds well to the direct bandgap transition ($n_{1\mathrm{\Gamma }}?n_{1HH}$). The light output power was about 2.0 μW with an injection current density of $200\mathrm{kA}/{\mathrm{cm}}^2$. These results show that the horizontal GeSn/Ge MQW ridge waveguide emitters have great prospects for group-IV light sources.